| Summary Information |
| Type of
technique |
Health
& Management / Bird
Husbandry and Management / Incubation of Birds /
Techniques: |
| Synonyms and
Keywords |
-- |
| Description |
Candling is the process of
monitoring embryo development within eggs by shining a bright light through the egg. A
torch (flashlight) with a cardboard tube on the top may be used, or a box constructed with
a bulb inside and an egg shaped hole on one side, preferably rubber-rimmed.
- An egg in which no development is visible is described as "clear". A
"clear" egg may be infertile, or has not been incubated long enough to develop,
or may have been fertile but the embryo died at a very early stage of development.
- A fertile egg appears pinkish or reddish compared to the orange yolk of a
"clear" (infertile) egg. (B115.4.w1)
- In a fertile egg a spot with a web of tiny lines radiating from it may be seen by
three days of incubation (for an egg of total incubation time 21days).
- By five days (of 21) a larger "spider" may be seen and the air space
noticeably increased in size; (clearly visible blob and veins by seven days in most
waterfowl eggs; B29)
- Pulsation may be visible by 7 of 21 days.
- The veins should extend around the yolk and eventually throughout the egg
- The developing embryo blocks out light passing through the egg, and the egg is
almost black by 15 of 21days, except for an obvious clear area (the air space) at the
blunt end (B41,
B115.4.w1,
B139).
- Movement of the embryo may be visible in eggs with a
light-coloured shell.
- The size of the air space at the blunt (large) end of the egg increases
considerably during incubation.
- A splotchy yellow and brown appearance indicates a dead embryo or an infected egg
(B115.4.w1).
- A dark red ring in an egg in the early stages of incubation indicates early
embryonic death or imminent death of the embryo (B115.4.w1,
B139).
- An irregular edge to the air space or an indistinct separation between the air
space and the rest of the egg may indicate an infertile egg or dead embryo.
- Sudden loss of the clear air space may be seen in hatching eggs, as the head and
neck of the chick enter the space (B139).
|
| Appropriate Use (?) |
- Incubated eggs should be candled regularly (once or twice a week) so that
infertile or dead eggs can be removed.
- Flotation may be used for eggs where shell thickness and pigmentation
make candling difficult or an adequate light source is not available.
|
| Notes |
- A stronger light source is needed for thicker shells and for pigmented shells.
- Candling is easier in a dark area.
- Good records including sketches and written descriptions will assist in
interpretation.
- Expected stages are reached later in eggs with a greater total incubation time.
For example the percentage of the egg which should be occupied by the air space will be
smaller at 14 days if the egg has an incubation period of 35 days (egg 2/5 of the
way through incubation) than if the incubation period is 21 days (egg 2.3 of the way
through incubation).
- If results of candling are uncertain, wait a week and re-check (B139).
|
| Complications / Limitations / Risk |
- Eggs left out of the incubator too long may become too cool.
- Eggs may become overheated while being candled, particularly if a high-power bulb
is used.
- It is more difficult to candle eggs with very thick or highly pigmented shells.
- Light leakage around the egg makes candling more difficult.
|
| Equipment / Chemicals required and Suppliers |
Appropriate light source |
| Expertise level / Ease of Use |
Interpretation of what can be seen
when an egg is candled improves with experience. |
| Cost / Availability |
Inexpensive. |
| Legal and Ethical Considerations |
- Rough handling, too long spent outside the incubator and too long spent close to
a hot light bulb may damage embryos.
- Neglecting to monitor eggs for development and remove dead or infertile eggs may
promote bacterial or fungal contamination of other eggs, with consequent losses of
eggs/chicks to infection.
|
| Author |
Debra Bourne |
| Referee |
|
| References |
B12.5.w10,
B41, B42, B106,
B108,
B115.4.w1, B139 |